1. Field of the Invention
The present invention relates to a flat display device for displaying an image by utilizing an electron beam, which is provided with a support arrangement for supporting a single faceplate and, particularly to a flat display device wherein a flat faceplate is provided, a fluorescent screen formed on the faceplate that is defined as a continuous arrangement of a plurality of segment regions, the respective segment regions are scanned by an electron beam, and one image is formed on the screen surface.
2. Description of the Related Art
In the prior art a cathode-ray tube has been used as a typical display device in which a fluorescent screen in a vacuum envelop is scanned by an electron beam and an image is displayed on the screen. In recent years, various studies have been made for a high definition broadcasting or a high resolution picture tube having a large screen. In order to obtain a high resolution of the picture tube, a spot diameter of the electron beam in the screen must be minimized. Conventional improvements have been made concerning the structure of the electrode of an electron gun, by enlarging the diameter of electron gun itself, and the elongation thereof, but have proven to be insufficient. The main reason lies in that the distance between the electron gun and the screen becomes longer as the diameter of the tube becomes large so that magnification of the electron lens becomes too large. In other words, in order to achieve high resolution, it is important to shorten the distance between the electron gun and the screen. For this purpose, the tube is designed as a wide angle deflection tube. However, in such a tube, the magnification at the center region of the screen differs from that at the peripheral region thereof.
Due to this, in Japanese Patent Disclosure No. 48-90428 and Japanese Patent Disclosure No. 49-21019, and Japanese Utility Model Disclosure No. 53-117130, there has conventionally been proposed a method for displaying a large screen image having high resolution by arranging a plurality of independent small-sized picture tubes. This type of method is useful for a huge screen image display having a large number of divisions, which is arranged outside. However, in a case of an intermediate large-sized screen display of about 40 inches, it is obvious that the displayed image is not clearly seen since the connecting portion of the screen of each region, that is, the connection portions between the small-sized picture tubes are conspicuous in particular, if such a display is used as a display terminal for a computer aided design (CAD) and graphics, it goes without saying that having such a connecting portion in the display screen is a decisive defect as a display device. To solve this problem, in U.S. Pat. No. 3,071,706, Japanese Utility Model Disclosure No. 39-25641, Japanese Patent Disclosure No. 42-4928, and Japanese Patent Disclosure No. 50-17167, there has been proposed the structure in which a plurality of independent picture tubes are integrated into a screen.
As shown in FIGS. 1A and 1B, a picture tube 1 comprises a vacuum envelop having the integrated screen structure comprises a faceplate 3 having a screen 2, a rearplate 4 opposing to the faceplate 3, a plurality of funnels 5, which is continuous to the rearplate 4, and a plurality of necks 6, which are continuous from the funnels 5, respectively. The faceplate 3 is made of glass, and the rearplate 4 is made of glass or metal. In the above-mentioned structure, if the screen 2 is enlarged, the faceplate 3 and the rearplate 4 must be considerably thickened to have a sufficient strength against atmospheric pressure. Also, large curvature in a direction of a tube axis must be provided. Due to this, the weight of the entire vacuum envelop becomes extremely heavy, and the screen 2 has curvature in the direction of the tube axis and the displayed image on the screen is not clearly seen. Moreover, the distance between the screen 2 and an electron gu assembly 7 received in the neck 6 becomes large, and this is unfavorable in view of the design of an electron lens.
In a case where the rearplate is made of metal, a method is known for forming a reinforcing plate from a relatively thin metal plate in order to maintain sufficient strength against atmospheric pressure and lighten the device. The metallic rearplate is very useful for a case where there is no projection member such as a funnel and a neck in the rear surface portion of the display device. Moreover, a conventionally complicated shape can be simply formed if a metallic plate is applied to the structure of an envelop of the display device such as a cathode-ray tube wherein funnels and necks are formed on the rear surface portion. However, in the cathode-ray tube wherein the funnels and the necks are connected to the rearplate and a fluorescent screen is dividedly scanned by a plurality of electron beams, the electron gun assembly and the fluorescent surface must be correctly placed at a predetermined position. However, the metallic rearplate is easily deformed by atmospheric pressure as compared with the glass rearplate. Due to this, the position of the electron gun is changed by the deformation of the metallic rearplate, and the electron beam can not be emitted from the predetermined position to the predetermined direction. As a result, definition of the display image is extremely reduced. Therefore, the metallic rearplate is useful for a display device, where there is no influence on an internal structure or a track of the electron beam, even if the rearplate is a little deformed. Yet in a case where such a metallic plate is used in the structure wherein the funnels and necks are formed in the rearplate, an amount of deformation must be calculated in advance and the electron gun must be arranged at a predetermined position after the deformation. This is unfavorable in view of the design and the manufacture of the cathode-ray tube.
Moreover, in the cathode ray tube in which the internal section of the envelop becomes an equipotential space having high potential, an electrically insulating structure must be formed in the inside of the rearplate, so as the high potential is not exposed outside. In the cathode-ray tube wherein the funnels and necks are connected to the rearplate, potentials are extremely high, and thus such structures are unfavorable for practical.
The glass molding which comprises the rearplate 4, which corresponds to the funnel of the conventional cathode-ray tube as shown in FIGS. 1A and FIG. 1B, cannot be shaped to have sharp angles and still possess sufficient strength to support against the atmospheric pressure. Therefore, the rearplate cannot help but be formed in order that the entire shape curves smoothly. Therefore, it is extremely difficult to form the shape of the portion, on which a deflection device is mounted, to be equal to the shape of a deflecting region of the electron beam. Also, it is extremely difficult to thin glass of the deflection device mounting portion. Therefore, it is impossible to use a small-sized deflection device having small deflecting electric power.
Moreover, even if there is used a cathode-ray tube in which a metal plate is used as a rearplate, the shape of the inner surface of a funnel of the portion where a deflecting yoke is mounted is made close to the track region of the actual electron beam, and the thickness of the funnel is formed to be thinned, the following disadvantages will occur.
An eddy current is generated in the metallic plates adjacent to the detection devices, and it is difficult to avoid generating loss by the eddy current. As a result, deflecting electric power increases. Moreover, in a case where the metallic plate is used, the metallic plate is structured to be arranged between the adjacent detection devices, and the magnetic fields of the deflection detection devices are easily interfered with each other. Due to this, it is extremely difficult to form a suitable distribution of the magnetic field.
In general, in the use of a vacuum envelop having a flat faceplate, it is well-known to use support members to support the faceplate having a large area in connection with a solar energy collecting device. Such a flat display device using the support members has been proposed in Japanese Patent Disclosure No. 56-106353, Japanese Patent Disclosure No. 62-272432, Japanese Patent Disclosure No. 62-285335, Japanese Patent Disclosure No. 63-128532, Japanese Patent Disclosure No. 48-90183, Japanese Patent Disclosure No. 64-10553, and Japanese Patent Disclosure No. 1-117251.
As shown in FIGS. 2 and 3, there are used long plate-like support members 11 or needle-like support members supporting against the atmospheric pressure, which is applied to a flat envelop 10 whose inside is vacuum exhausted. The long plate-like support members 11 are used in order to prevent load of atmospheric pressure from concentrating on one point by supporting a screen 12 at the large contact area. An inventor found out various problems in the structure having the long plate-like support members 11 as a result of the various experiments.
First, there is a problem in accuracy of processing the support members. In this structure, as shown in FIG. 4, an end portion 11a of the support member, which contacts the screen along a black stripe 12a of the screen, must be processed to be shaped like a knife-edge. Furthermore, it is necessary to completely conform the distance between the faceplate and the rearplate to the length of the support members, that is, the height thereof. If a length of the knife-edge portion along the longitudinal direction thereof is about 30 mm or less, such a process can be practically performed, that is, such a process can be performed in terms of quantity. However, if the length thereof is more than 30 mm, a special process is required, and the device cannot be manufactured at low cost.
Second, there is a problem in strength of the plate-like support members. In the use of the plate-like support members, strength is large in a case where load is applied in a direction parallel to the surfaces of the plate-like support members. However, if load is applied in a direction, which is inclined to the surfaces, the plate is easily deformed and excessive load is applied to the other adjacent support members.
Third, there is a problem in a method for fixing the plate-like support members. Since the plate-like support members cannot stand itself, there is required a member for setting up the plate-like support members to be perpendicular to the rear panel, or a fixture in a case of welding in order to attach the plate-like support members to the rear panel.
Fourth, there is a problem in deformation. The plate-like support members are strong against the deformation in a direction in a surface, but easily deformed in the direction other than the inner surface direction. As shown in FIG. 5, deformation 11b is easily generated during a fixture or a heating process.
Fifth, there is a problem in the contact between the plate-like support members and the sheet glass. Since the normal sheet glass is manufactured by a float method, it is impossible to completely equalize the thickness of the whole sheet glass. Regarding the distribution of the thickness of the sheet glass, there is no difference in the thickness in the relatively narrow portion, for example, about 50 mm. However, in the relatively large portion, for example, about 200 mm, a difference in thickness can range from 0.05 mm to 0.1 mm. In other words, even if the plate-like support members are accurately processed and assembled, the complete contact between the plate-like support members and the sheet glass serving as a faceplate is not always made.
Regarding the needle-like support members, the following problems exist:
First, there is a problem in the required number of needle-like support members, needed to support against the atmospheric pressure. In the plate-like support members, the contact area between the plate-like support members and glass is relative large. In contrast, the contact area between the needle-like support members and glass is extremely small, and therefore a considerably large number of needle-like support members are needed in order to reduce load weight of each support member. More specifically, the needle-like support members must be arranged with a pitch of 10 mm or less, and a 1000 or more needle-like support members are needed in order to support against the atmospheric pressure applied to the sheet glass whose size corresponds to 20 inches of the diagonal size of the screen.
Second, there is a problem in accuracy of processing. According to this method, the top end portion of the member must be processed to be needle-like. Generally, a method for processing a wire material to be needle-like can be easily processed by a cylindrical grinding. However, it is difficult to accurately position the central axis of the wire material and the top end portion portion of the processed needle-like member, and there often occurs cases where the central axis of the wire material and the top end portion are eccentrically processed.
Third, there is a problem in strength of the needle-like support members. Similar to the case of the plate-like support members, strength is adequate in a case where load is applied in an axial direction of the wire material. However, if load is applied in a direction, which is inclined to the axis, the plate is easily deformed and excessive load is applied to the other adjacent support members.
Fourth, there is a problem in a method for fixing the needle-like support members. Similar to the case of the plate-like support members, since the thin needle-like support members cannot stand by themselves, there is required a member for setting up the needle-like support members to be perpendicular to the rear panel, or a fixture in a case of welding in order to attach the needle-like support members to the rear panel.
As mentioned above, the plate-like or needle-like support members are not favorable for practical use in view of the structure, manufacturing, assembling, and the cost. Moreover, the conventional flat cathode-ray tubes, which have been proposed, include a large number of wire cathodes 13, a large number of control electrodes 14, accelerating electrodes 15, deflecting electrodes 16 therein. The structure is very complicated, and there are many problems in the manufacture. If the large-sized screen is used, the manufacture of the cathode-ray tube becomes extremely difficult. Moreover, since it contains a large number of support members and inner electrodes, there occurs a problem on occluded gas of these members. As a result, a life characteristic of the cathode-ray tube is largely deteriorated, and this is considerably unfavorable for practical use.
As mentioned above, there are various problems in the prior art to obtain a cathode-ray tube having high resolution, a small depth, good visible image, simple structure, high practical use, and high industrial value.